Many different dentifrice compositions are known for cleaning, whitening, and preserving the teeth. Of these known dentifrices, many include water-insoluble abrasives such as calcium carbonate, dicalcium phosphate, tricalcium phosphate, calcium pyrophosphate, sodium metaphosphate, or corresponding magnesium salts, which act as polishing agents for the teeth. Conventional cream or paste dentifrices containing such abrasives are opaque.
Since the ultimate goal of any oral hygiene regimen is preservation of the teeth, it is widely accepted that dentifrice compositions should include polishing agents having the minimum abrasivity consistent with good cleaning characteristics. Sodium bicarbonate is a desirable abrasive from this standpoint since it is low in abrasion and imparts an exceptionally clean, fresh feel to the mouth. Sodium bicarbonate particles are relatively soft as compared to most conventional abrasive materials used in dentifrice compositions. Thus, the American Dental Association has recommended that if only a slight degree of abrasion is necessary to keep teeth from staining, baking soda is usually a satisfactory abrasive. Accepted Dental Therapeutics, pages 340-41 (38th Ed., 1979).
Sodium bicarbonate has, accordingly, previously been used as an abrasive in dentifrices. Thus, sodium bicarbonate has both been described in the literature as an ingredient of tooth powders (see Winston, et al, U.S. Pat. No. 4,547,362 and 4,663,153 owned by the assignee of the present invention) and toothpastes and dental creams (see Delaney, U.S. Pat. Nos. 3,935,305; 3,927,321; 3,937,803; 3,937,804; and 3,943,240; and Winston, et al, U.S. Pat. Nos. 4,623,536 and 4,721,614, owned by the assignee of the present invention); and has been incorporated in commercial tooth powders and toothpastes (ARM & HAMMER DENTAL CARE tooth powder and toothpaste, and COLGATE PEAK).
In recent years, gel dentifrices have gained substantial popularity in the dentifrice market. They provide a esthetic appeal which frequently connotes mouth freshening to the consumer. Such translucent gels are produced when the polishing agent or agents incorporated therein have substantially the same refractive index as the gel vehicle. See Colodney, U.S. Pat. Nos. 3,906,090 and 4,036,949, and Harrison U.S. Pat. No. 3,911,102. Typical of the abrasives which may be used in such gels are the hydrated silicas and the synthetic amorphous complex aluminosilicate salts of alkali metals or alkaline earth metals which have refractive indices of about 1.45-1.50.
Since the refractive index of water is only about 1.33, the liquid carriers for gel dentifrices generally contain humectants such as glycerin or sorbitol which have higher refractive indices (1.45-1.50) and which increase the refractive index of the carrier to about that of the polishing agent. One such dentifrice gel having a balanced refractive index is described in Harvey, et al, U.S. Pat. No. 3,927,202. Harvey discloses gels incorporating up to 50% of an alkali metal phosphate polishing agent having a refractive index between 1.435 and 1.465, in a vehicle comprising from 20% to 80% of a water-humectant mixture and from 0.5-10% of a gelling agent in proportions such that the vehicle has a refractive index of between 1.36 and 1.47. (Harvey, col. 1, lines 40-57).
Sodium bicarbonate has three indices of refraction (i.e., 1.376, 1.500, and 1.58; see Handbook of Chemistry and Physics, 66th Ed., CRC Press (1985)). These disparate indices differ so markedly that it is impossible to reasonably closely match the refractive indices thereof with any liquid carrier, in order to provide a translucent gel.
It is, accordingly, among the objects of the present invention to provide a sodium bicarbonate-based dentifrice gel which, notwithstanding differences in the refractive indices of the ingredients thereof, is nevertheless wholly or partially transparent. Other objects and advantages of the invention will be apparent from the following description of preferred embodiments thereof.